Pediatric Dosing

Question 0

Developmental physiology

Answer 0

1. Ribs extend horizontally from vertebral column compared to cauded angel in adults

• this renders the accessory muscles of respiration ineffective in infants
• Ribs tend to move inward with inspiration due to high cartilage content
  
  • this paradoxical chest wall movment occurs commonly under anesthesia and its due to :
    
    • decrease in tone of intercostal muscle
    • upper airway obstruction
  • Diaphram increases its work to maintain tidal volume, which can lead to fatigue
    
    • mature diaphram has low contect of type I muscle fiber (slow twich, high oxidative capacity
      
      • before 37 week gestation 10% type I
      • full term infant 25%
      • aduly 50%
        
        • This means that diaphram is more likely to become fatigues in premature and term infants leading to earlier respiratory failure
• Chest wall compliance:
  
  • decreases throughout childhood and adolescence due to
    
    • ossification of the ribs
    • development of thoracic muscle mass
• Elastic recoil pressure of lungs:
  
  • increases throughout this time due to increase in pulmonary elastic fibers

Question 1

Pediatric dosages

Answer 1

Roc: 0.6 mg/kg Fentanyl: dilute 100 in 10 cc 1-2 mcg/ kg Acetaminophen: 15 mg/ kg Dex: antiemetic: 0.15 mg/kg Anti inflammatory: 0.25 mg/kg Ketorolac: 0.5 mg/kg Succynilcholine: 2mg/ kg/ 4 mg/ kg IM Atropine: 0.02 mg/ kg IV/ 0.04 mg/ kg IM

Question 2

Respiratory variability btw children and adults

Answer 2

1. Total lung capacity (TLC) is much larger in adults/kg compared to infants
   * Mainly due to efficiency and strenght of inspiratory muscles in adults
2. Functional residual capacity (FRC)

• FRC:
  
  • Volume at which passive elastic recoil of the chest wall are balanced by recoil of the lung. This is the volume at the end of exhilation
  • Functional Residual Capacity (FRC) is the volume of air present in the lungs, specifically the parenchyma tissues, at the end of passive expiration.
  • At FRC, the elastic recoil forces of the lungs and chest wall are equal but opposite and there is no exertion by the diaphragm or other respiratory muscles.
  • FRC is the sum of Expiratory Reserve Volume (ERV) and Residual Volume (RV) and measures approximately 2400 mL in a 70 kg, average-sized male
  • A lowered or elevated FRC is often an indication of some form of respiratory disease. For instance, in emphysema, the lungs are more compliant and therefore are more susceptible to the outward recoil forces of the chest wall. Emphysema patients often have noticeably broader chests because they are breathing at larger volumes. In healthy humans, FRC changes with body posture. Obese patients will have a lower FRC in the supine position.
• Similar on per kg basis among age groups but mechanical reason for it is diff
  
  • In infant the elastic recoil of chest and recoil pressure of lung are very small
    
    • this would predict and FRC of 10% however actual FRC is 40%
      
      • due to increase in expiratory time constant process known as laryngeal barking

3. Lung volume:
   * Less than FRC–> apneic infant has smaller store of intrapulmonary o2 than adult and hypoxia will develop rapidaly if ariway is poorly maintained
4. Closing capacity:

• CC is larger than FRC, so during exhilation small airways start to collapse and trap air.
  
  • note: in adults closing capacity is smaller than FRC

Question 3

Factors affecting respiration

Answer 3

1. infants like adults Pao2, Paco2 and PH control ventilation

• increase in Paco2 increases min ventilation by increasing tidal volume and respiratory rate
  
  • this responce to hypercapnia is not enhanced by hypoxia
  • hypoxia may depress the hypercapnic ventilatory responce
• High insipired O2 (Pao2) depress new born respiratory drive
• low inspired O2, stimulates the respiratory drive
  
  • however continued hypoxia will eventually lead to repiratory depression
  • Hypoglycemia, anemia, and hypothermia will also decrease respiratory drive

2. Metabolic demand drives min ventilation

• as O2 demand goes up, min ventilation also increases
  
  • more increase in respiratory rate than tidal volume

Question 4

Intraoperative fluid maintenance

Answer 4

1.Intravenous fluid given in operating room has 4 purposes:

• replacement of fluid deficiet
  
  • Number of hours patient was NPOx hourly maintenance fluid requirment
  • 50% of deficiet is replaced in first hour, remainiing 50% in next 2 hours
  • emergency surgery may have larger fluid deficiet due to blood loss, third space loss, fever and vomitting
• maintenance
  
  • hourly maintenance is by 4-2-1 rule
  • <10 4ml/kg
  • 11-20 40+2ml/kg
  • >20 60+1ml/kg
• balancing ongoing losses
  
  • whole blood loss
    
    • 1:1 replacement when blood of colloid used
    • 3:1 when chrystaloids are used
  • this space loss and evaporation:
    
    • depends on type of surgery
      
      • non-invasive 0-2 ml/kg/hr
      • mildly invasive 2-4 ml/kg/hr
      • moderatly invasive 4-8 ml/kg/hr
      • significantly invasive: > 10 ml/kg/hr
• treatment of hypovolemia
  
  • tachycardia+hypotension=hypovolemia
  • 10-20 ml/kg bolus of crystaloids can be given

2. Intravenous fluid used:

• non-glucose containing isotonic solution
  
  • to avoid hyponatremia ( low sodium concentration in blood)
  • lactated ringer most commonly used

Question 5

Pediatric airway

Answer 5

watch out for the following:

1. micrognathia
2. midface hypoplasia

Question 6

Pediatric airway anatomy

Answer 6

1. infants and children have larger cranium–> unnecessary to place a pillow under occipit to achieve sniffing position
2. Tongue relatively large can more early obstruct the airway
3. cricoid ring is thought to be the narrowest part of the airway instead of vocal cords in adults
   * however recent MRI and bronchoscopic data indicate that pediatric airway is cylindrical and narrowest part is in glottis as in adults
4. Larynx is relatively higher at C4, rather than C6 in Adults
5. epiglottis is omega shaped and soft as oppose to U shaped and still in adults